In the related art, a vehicle seat reclining apparatus described in JP 2009-95432A (Reference 1) is known as such a vehicle seat reclining apparatus. As shown in FIG. 8, the vehicle seat reclining apparatus includes a gear arm 101 having inner teeth 101a, a support arm 102 supported by the gear arm 101, poles 103 whose movement in the radial direction is guided by guide portions 102a provided on the support arm 102, a cam 104 engaging the poles 103, and a locking spring 105 configured to urge the cam 104 to rotate.
The cam 104 includes a hinge pin 106 fitted thereto. In other words, so-called an oval shaped engaging hole 104a having two inner side surfaces parallel to each other is formed at a center portion of the cam 104. In contrast, the hinge pin 106 is formed with a shaft portion 106a whose column-shaped outer peripheral portion is chamfered along two flat surfaces parallel to each other. The hinge pin 106 penetrating through the engaging hole 104a of the cam 104 is configured to engage the engaging hole 104a of the cam 104 in two chamfered portions of the shaft portion 106a (hereinafter, referred to also as “width cross flat”). Then, the shaft portion 106a of the hinge pin 106 is provided with an operating lever (not illustrated) integrally attached thereto.
In such a configuration, if the poles 103 guided by the support arm 102 (the guide portions 102a) are advanced in the radial direction by the rotation of the cam 104 urged to rotate by the locking spring 105, the inner teeth 101a of the gear arm 101 and outer teeth 103a of the poles 103 engage, so that the rotation of the gear arm 101 with respect to the support arm 102 is restricted. Alternatively, if the poles 103 guided by the support arm 102 (the guide portions 102a) are retracted in the radial direction by the rotation of the cam 104 via the hinge pin 106 in association with a release operation of the operating lever, the inner teeth 101a of the gear arm 101 and the outer teeth 103a of the poles 103 are released, so that the rotation of the gear arm 101 with respect to the support arm 102 is allowed. With the configuration described thus far, the rotation of the seatback with respect to the seat cushion is restricted or allowed to adjust and maintain the seatback to a required angle of inclination suitable for seating of a passenger.
In JP 2009-95432A (Reference 1), the shaft portion 106a of the hinge pin 106 penetrates through the engaging hole 104a with a gap formed with respect to the engaging hole 104a of the cam 104. It is for absorbing inclination of an axial line of the hinge pin 106 if any by the gap formed with respect to the engaging hole 104a and preventing an axial line of the cam 104 from inclining together with the hinge pin 106. Accordingly, the rotation of the cam 104 and advancement and retraction of the poles 103 associating therewith are smoothened, and an operation when restricting or allowing the rotation of the gear arm 101 with respect to the support arm 102, that is, an operation when restricting or allowing the rotation of the seatback with respect to the seat cushion is further stabilized.
However, in this case, there arises a circumferential play in the circumferential direction between the width across flat of the shaft portion 106a relating to the transmission of rotation between the hinge pin 106 and the cam 104 and both of the inner side surfaces of the engaging hole 104a parallel to each other. Therefore, a remarkable lag (that is, an operation loss) is generated between rotation start timing of the hinge pin 106 in association with the release operation of the operation lever and timing of a release of engagement between the inner teeth 101a of the gear arm 101 and the outer teeth 103a of the poles 103 in association with the rotation of the cam 104, whereby operation feeling may be degraded.
A need thus exists for a vehicle seat reclining apparatus which is not susceptible to the drawback mentioned above.